X-ray hoisting apparatus with automatic securing means



R. T. AVERY March 23, 1965 X-RAY HOISTING APPARATUS WITH AUTOMATICSECURING MEANS Filed July 13, 1961 4 87 2 4 4 W Y m M 1 TE Y 7 I NV n E8 5 W N 5 T T R A a x 3 v 0 l 5 2 R an Y B 4 9 7 I %4 6 72 w 3 4+ 4 9 181 I r 8 z \I. \k 5.\ s a Q 5 2 I a l l\ G \100 F 7 1 u/l HY 5l/ 4 1 8mu 4 I I I MW t 4 5 W Mm %%4+ United States Patent Ofiiice 3,175,085Patented Mar. 23, 1965 3,175,085 X-RAY HOISTING APPARATUS WITH AUTO-MATIC SECURING MEANS Robert T. Avery, Los Altos, Calif, assignor toVarian Associates, Palo Alto, Calif., a corporation of California FiledJuly 13, 1961, Ser. No. 123,855 31 Claims. (Cl. 250-91) This inventionrelates to a hoisting apparatus for supporting and for transporting aheavy object and, more particularly, to a depending boom hoist to whichthe object is attached and which supports the object rigidly when theobject is at rest.

In very specialized applications, a high energy X-ray machine must besupported on the end of a depending rigid boom hoist which is moveableon overhead tracks. The boom must not only be capable of transportingthe X-ray machine but must motionlessly and rigidly secure the machinewhile X-ray pictures are being taken. Also, any inherent oscillation inthe hoist must be quickly dampened when the X-ray machine comes to rest.A typical high energy X-ray machine is described in U.S. patentapplication No. 46,432, filed on August 1, 1960, now abandoned, in favorof continuation US. patent application Serial No. 411,170, filed onSeptember 14, 1964, by the same inventor and assigned to the sameassignee as this application. The X-ray machine comprises a linearaccelerator which accelerates electrons to high en ergies (in the orderof eleven million electron volts) and means which then direct the highenergy electrons onto a target to produce very high energy X-rays. Theelectron beam is also focused to a very small cross section in theregion of the target so that a point X ray source is simulated which, inturn, will produce very sharp pictures. The high energy linearaccelerator, as described in the above application, is long and heavyand mobility is provided in the above accelerator by mounting theaccelerator transversely onto the end of a telescoping boom dependingfrom an overhead trolley hoist. The electron beam axis is disposedhorizontally and rotates about the vertical axis of the boom.

Since an electron beam cannot be focused to a mathematical point, theelectron beam in this accelerator is focused to a small area having adiameter of less than one millimeter thus making a one millimeter X-raysource. A person skilled in the art of producing X-ray picturesunderstands that the boom will oscillate when the X-ray machine comes torest. These oscillations must be quickly dampened and the inherentamplitude of vibration of the X-ray source must be limited, for example,on the order of one-half of a millimeter or one-half of the diameter ofthe X-ray source size so that maximum resolution on the X-ray pictureswill be obtained. To do this, when the X-ray source is positioned totake an X-ray picture, its supporting member must be immoveable. Therecan be no play between the moveable parts of the boom and of the hoist,and the supporting member must have sufiicient stiffness to maintain theamplitude of vibration within acceptable limits. The amplitude ofvibration of the X-ray source is inversely dependent on the moment ofinertia of the boom and directly dependent on the weight of the X-raysource. With the large moveable parts necessary to decrease theamplitude of vibration,,there must be suflicient clearance between themso that they do not bind during positioning of the X-ray source. Thisclearance or play between the moveable parts must be automatically takenup when the X-ray source is in position as it would be impractical tomanually clamp the sections together before an X-ray picture is taken.The take up means substantially restricts relative transverse motionbetween the telescoping sections both in the movement thereof and whenin a fixed position.

The principal object of this invention is to provide a moveable supportstructure which will motionlessly and rigidly support a large objectafter the object has been moved into a desired position by the supportstructure.

One feature of this invention is the provision of a moveable supportstructure arranged to rotate a large object about a vertical axiswithout backlash.

Another feature of this invention is the provision of a slip drive toperform the above rotation without backlash.

Another feature of this invention is the provision in the above moveablesupport structure of a flat drive sprocket coaxially disposed between afixed support on the support structure and a flanged shaft wherein athrust force in the shaft forms a friction brake between the flange onthe shaft and the sprocket and between the sprocket and the fixedsupport.

Still another feature of this invention is the provision of a moveablesupport structure in the form a of a telescoping boom wherein the playbetween the separate boom parts is taken up and eliminated.

Another feature of this invention is a track and a springloaded followerbetween sections of a telescoping boom to take up the play between thesections.

Another feature of this invention is a telescoping boom wherein thesections are fixed with respect to each other at all stationary boompositions.

These and other features and advantages of the present invention will bemore apparent after a perusal of the following specification taken inconnection with the accompanying drawings wherein,

FIG. 1 is a view in elevation of an extended vertical boom supporting alinear accelerator with both the boom and accelerator supported by anoverhead trolley hoist,

FIG. 2 is a cross sectional view taken on line 2-2 of FIG. 1 with thecenter block and tackle removed.

FIG. 3 is an enlarged partial sectional view of the boom enclosed bycircle 3-3 of FIG. 1,

FIG. 4 is an enlarged partial sectional view of the boom depicted inFIG. 1, and

FIG. 5 is a cross sectional view taken on line 5-5 of FIG. 4.

Referring to FIG. 1 a linear accelerator 12, including its power supplyenclosed in a cabinet 13 and an X-ray head unit 14, is supported on thebottom end of the ver-, tically disposed hollow boom 15 which is, inturn, mounted on an overhead trolley hoist assembly 16. The hoistassembly 16 comprises a square frame 17 to which the boom 15 is fixedand suitable wheels 18 that ride on I- beam tracks 19 which are part ofan overhead-disposed moveable-beam 20. An electric motor 21 mountedwithin the hoist 16 powers the wheels 18 to provide horizontal motion inone direction for the accelerator 12 along tracks 19. The overheadmoveable beam 20 is mounted on other tracks (not shown) for horizontalmotion normal to the one direction. A flexible conduit means 22 extendsfrom the overhead 20 to the accelerator 12 through the hollow boom 15.The conduit means supply electrical energy and cooling water to theaccelerator 12.

The boom 15 is made of a plurality of telescoping sections, and as shownin this embodiment, includes three sections, an upper section 23, fixedto the frame 17, a middle section 24, and a bottom section 25 whereinsection 25 nests within section 24 which, in turn, nests within section23. Another electric motor and hoisting drum (not shown) powers a blockand tackle 26 (shown by dash lines) to provide vertical motion to theaccelerator 12. The lower pulley of the block and tackle 26 is attachedto a diagonal brace 27, shown partially broken away in FIG. 2.

The accelerator 12 is'rnounted with its beam axis horizontal; the powersupply cabinet 13 at one end balance the heavy X-ray head 14 at theother end. The linear accelerator 12 is rotatable upon a vertical axiswhich coincides with the axis of the boom 15 and is supported by thebottom section of the boom through a shaft 28 (FIG. 3) which has one endfixed to the linear accelerator 12 through a triangular supportstructure. Shaft 28 is preferably made tubular so that the flexibleconduit means 22 conveniently passes therethrough to the accelerator 12.The triangular support structure comprises a sleeve 29 and four radiallyprotruding I-beams 30 fixed to the frame of the linear accelerator 12and four anglemembers 31 equally spaced about the sleeve 29 and eachsecured at one end to the sleeve 29 and at the other to the :outer endof one of the Lbeams 30. The shaft 28 fits snugly within the sleeve 29as a shear pin 32 passes through both the sleeve 29 and shaft 28 tosecure the two together.

Shaft 28 is rotatable within another sleeve 33 disposed within and fixedto the boom bottom section 25. Sleeve 33 is welded to a transverse steelplate 34 and braced by four angle members 36 equally spaced about sleeve33. a On its upper end the shaft 28 has a radial flange 37 which bearson an enlarged steel thrust washer 38 which has a journal bearingsurface 39 attached thereto. The radial flange 37 could have been madelarger wherein it'will have the same diameter of thrust washer 38 and,therefore, eliminating washer 38. The embodiment illustrated ispreferred because machining time is saved since a smaller shaft 28 wasused. The bearing surface 39 bears on one of the opposing parallelsurfaces of a gear 41, theaxis of the gear 41 coinciding with the axesof the shaft'28 and sleeve 33. Gear 41 rests on a combination radial andthrust journal bearing 42 press-fitted into the upper end of the sleeve33 to form a thrust journal bearing with the upper end-face of bearing42. The inner cylindrical surface of bearing 42 forms a radial journalbearing for shaft 28. A radial journal bearing 43 is pressfitted at theother end of sleeve 33 also to provide alignment and a suitable bearingbetween sleeve 33 and shaft 28. The gear 41 is rotated about itsvertical axis by electric gear motor 44 acting through a sprocket 45.The sprocket 45 is connected to gear 41 through a chain 46.

Since the linear accelerator must also be raised or lowered by the boom15, the telescoping boom sections, therefore, are made to move axiallyrelative to each other and nest, as mentioned above, within each other.Suitable clearance must be provided between the sections so they canmove freely. The clearance must also be taken The clearance and freeaction which is required between the sections is provided by suitabletracks 47, FIG. 2, which are made from rectangular cross-sectioncoldrolled steel. Tracks 47 are disposed vertically near the corners ofthe sections 24 and 25 which have a square cross section. Although onlytwo tracks can be used on one section, four tracks on one section areused in the preferred embodiment, as shown, to prevent excessivetwisting of the sections. The top section 23 being an external sectiondoes not require any tracks 47. Each of the sections 23, 24 and 25include four steel angle sections 48 at each corner thereof, andsuitable stiifening brackets 49 are welded to the angle sections 48. Foraesthetic reasons, the sections are covered with a sheet metal cover 50.For convenience and strength, the tracks 47 are fixed to the cornerangle sections 48. Followers 52, preferably in the form of rollers, rideon tracks 47. A pair of rollers 52 is mounted on a lever 53 (FIG. 5) bysuitable bearing axles 54 and a pair of levers 52 are provided for eachtrack 47. Each lever 53 is pivotly mounted by means of pivot shaft 55disposed on the interior wall of a boom section, such as sections 23 and24 which surround another boom section. The rollers 52 and tracks 47provide the necessary friction-free clearance between the sections sothat they can move relative to each other without binding. The playbetween each pair of rollers 52 and tracks 47 is eliminated by pivotingthe lever 53 on its pivot shaft 55 disposed between two rollers 52 tocause each roller 52 to bear against the track 47 with a large constantforce. The large constant force is provided by a take-up means 57 (FIG.4).

The take-up means 57, in this embodiment, preferably comprises a pair ofthe levers 53 for each track 47. Since the tracks 47 are mounted only onthe inner boom sections, then to provide maximum stiffness and travelthe pairs of levers 53 are mounted near the bottom of the outer boomsections and on two horizontal angle braces 58. A vertical member 59 isWelded at its end to both braces 58 and the free ends of levers 53 areretained within U-shaped straps 61 that are welded by their ends tomember 59. The take-up means 57 are preloaded in this embodiment by atension spring 62 connected to both levers 53 in each pair to place atorque on the levers by urging the ends of the levers 53 toward eachother. The mechanical advantages of the levers 53 cause the rollers 52to maintain their contact with track 47. Since the weight of the upperlever 53 of each pair adds to the torque, the spring 62 is connected tothe lower lever at a point positioned further from the pivot shaft 55than the point where the spring is attached to the upper lever. Thus,all the rollers 52 bear against the tracks 47 with approximately equalforce.

Also, to insure that the X-ray head 14 is stationary, the telescopingcoaxially disposed boom sections 22, 24 and 25 must be always at givenstable, relative vertical position to each other when the unit 14 is ata given elevation. If the sections do not move under positive controlwith respect to each other, one of the sections may fall to lower levelat an inopportune time such as during an X-ray exposure. Positivecontrol means are provided for between the telescoping section in thisembodiment by an endless wire rope 65 engaging two spaced pulleys 66 and67 mounted on the middle section 24. For more uniform operation betweenthe sections, two sets of wire ropes and pulleys disposed on oppositesides of section 24 are used in this embodiment (FIG. 2). The pulleys 66and 67 are disposed near the ends of the center section 24 and make anangle of approximately with the sheet metal so that the pulleys protrudethrough the walls of the section, and the rope is, therefore, accessiblefrom the Outside as well as from the inside of the section 24. The outersection 23 is fixed and attached to the rope 65 with the aid of abracket 68 in a form of a steel plate that is welded to the section. Astandard U-shaped rope clip 69 encircles and clamps the rope 65 and isbolted to the bracket 68. The bottom inner section 25 is also fixed tothe rope 65 with the aid of another rope clip 71 which encircles andclamps the rope 65 and is bolted to the bracket 72. Of course, for fullvertical motion, the lengths of rope on either side of one clip 69 tothe other clip 71 are made equal to each other. While bracket 68 isdisposed near the bottom of section 23, bracket 72 (FIG. 2) is disposednear the top of section 25.

The accelerator 12 is free to rotate about a vertical axis, and a safetymeans is required to limit the angular motion of the accelerator so thatthe flexible conduit means 22 is not twisted excessively. The safetymeans includes an arm 76 (FIGS. 2 and 3) extending from a ring 77 thatfits loosely around the flange 37 of the rotating shaft 28. The ring 77is held in place with a collar 73 suitably bolted to the flange 37. Thecollar rotates with the shaft 25 while the ring 77 and arm are free fromthe shaft 28 but move within limits that are PIE? scribed by a lug 79extending up from the arm 76 engaging a lug 81 depending from the collar78. Thus, when the shaft 28 rotates a given number of degreescounterclockwise (FIG. 2), the lugs 79 and 81 make contact swinging arm76 to make contact with a microswitch 82 supported by a bracket 83 thatis welded to plate 34. The microswitch then stops the motor 44. Theshaft 28 can now be rotated clockwise and when it has turnedapproximately 360", the lugs 78 and 81 again make contact causing arm 76to contact another microswitch 82' (of which only the contact tip isshown in FIG. 2) similarly mounted on a bracket as microswitch 82. Themicroswitch 82 also stops the motor. The exact number of degrees throughwhich the shaft 28 can rotate is ad justed by the location of themicroswitches 82 and 82 and the geometry of the arm 76 and lugs 79 and$1. If the microswitches fail to stop the motor 44, arm 76 is stopped byeither of the support brackets for the microswitches 82 and 82 causingthe gear 41 to slip on bearing surfaces 39. The rotational limit meansis also useful to limit the angular displacement of the shaft toconsiderably less than 360, for example, the X-ray beam can be directedtowards only one wall of the room. This arrangement allows for aconsiderable savings in construction cost of the Xray room since heavyshielding is then required in only one wall instead of all four walls.

An operator operates the X-ray machine from a remote control means. Whenmotor 44 is started, sprocket 45 rotates causing the chain 46 to drivethe gear 41. The gear 41 slips across bearing 42 on top of the sleeve 33since it is fixed to the lower section 25, but the friction forcebetween bearing 39 and gear 41 is sutficient to cause shaft 23 torotate. When motor 44 stops, the friction force between bearing 39 andgear 41 and between gear 41 and bearing 42 provides a braking action toprevent any relative movement between the accelerator and the lower section 26. If the accelerator happens to be stopped by a wall or otherimmoveable objects while motor 44 is rotating it, bearing 39 will slipacross the gear 41 because the friction force being low is overcomewithout damaging the accelerator. In this embodiment, bearing surfacesare between steel and porous bronze and provide a suitable coeflicientof friction to maintain the necessary degree of friction wherebysufficient locking and also bearing is provided between the parts.

When the accelerator 12 is being raised, the rollers 52 that are mountedon top section 23, will roll in contact with the tracks 47 on section24. Any variation in the cross section of the tracks 47 will be taken upby levers 53 since they can pivot about the pivot 55 and move close toor away from the tracks. When the accelerator 12 stops, the spring 62tightens the rollers 52 against the tracks locking the two sections 23and 24 together. A similar motion is provided between sections 24 and25.

As the accelerator 12 is raised, section 24 moves into section 23 at thesame rate as section 26 moves into section 24 because of the action ofthe wire rope 65 and pulleys 66 and 67 arrangement. Then, when theaccelerator steps, so do all the sections stop and cannot move. If morethan three telescoping sections are required, the rope and pulley meansmust be installed on all sections disposed between two other sections.

Horizontal motion is provided in one direction by motor 21 turningwheels 18 whereby the wheels 18 travel along track 19. The wheels 18 aredisposed at the corners of the frame 17 whereby pendulum action in theboom is eliminated or substantially reduced.

Since all structural units can oscillate at a resonant frequency whichcan cause the unit 14 to oscillate as a pendulum, the boom 14 was madeinto a square cross section and stiffened sufiiciently to increase itsmoment of inertia so that the amplitude of vibration of the unit 14 ismaintained within prescribed limits. Since most of the play is taken upbetween the moving part, the amplitude can be readily limited withoutincreasing the size of the boom beyond reasonable limits. A telescopingboom was built to support an accelerator unit which can be extended toat least 25 feet from the overhead and weighed at least 9000 pounds. Theamplitude of oscillation was dampened to ,1 of an inch within less than20 seconds.

Since many changes could be made in the above construction and manyapparently widely different embodiments of this invention could be madewithout departing from the scope thereof, it is intended that all mattercontained in the above description or shown in the accompanying drawingsshall be interpreted as illustrative and not in a limiting sense.

What is claimed is:

l. A hoisting apparatus comprising a telescoping boom having at leasttwo coaxial sections including an inner section nesting within an outeradjacent section, means for supporting an object on one end of saidboom, means for rotating said object about the axis of said boom trackand follower means on said sections for guiding said inner sectionwithin said adjacent outer section, and take up means for securelyclamping said inner and outer sections together automatically when saidsections are stationary said take-up means also substantially restricttransverse relative motion, with respect to the boom axis, between saidsections both when said sections are moving relative to one another andwhensaid sections are stationary.

2. The hoisting apparatus of claim 1 wherein said followers are rollerswhich roll on said track.

3. The hoisting apparatus of claim 1 wherein said track follower meanscomprises a track on said inner section and followers on said outersection, said followers being disposed adjacent the end of said outersection closest to said inner section.

4. The hoisting apparatus of claim 3 wherein said take-up meanscomprises preloaded followers.

5. A hoisting apparatus comprising a telescoping boom having at leasttwo sections, including an inner section nesting within an adjacentouter section, means for supporting an object on one end of said boom,means for rotating said object about the axis of said boom, track andfollower means on said sections for guiding said inner section withinsaid adjacent outer section, and'take-up means for securely clampingsaid inner and outer sections together automatically when said sectionsare stationary, said track and follower means comprising a track on saidinner section and followers on said outer section, said followers beingdisposed adjacent to end of said outer section closest to said innersection, said take-up means comprising a lever means including a leveron which at least two of the followers in the form of rollers aremounted, said levers pivotally mounted on said outer section, one ofsaid tracks disposed between two of the roller followers on said lever,and means for applying a moment on said lever whereby said followersbear firmly against said track.

6. The hoisting apparatus defined in claim 5 wherein said lever meansfurther includes a pair of said levers with said roller followersengaging said one of said tracks and a spring attached to the ends ofsaid pair of levers and disposed on the same side of said track.

7. The hoisting apparatus as defined in claim 6 wherein said spring isattached to one of said levers of said pair closer to its pivot mountthan said spring is attached to the other of said levers whereby agreater moment is placed on said other lever than on said one lever.

8. A hoisting apparatus comprising a boom, means for supporting anobject on one end of said boom, means for rotating said object about theaxis of said-boom, said means comprising a shaft disposed to rotateabout said axis, said shaft bearing against a drive gear, said drivegear bearing against said boom, means for rotating said drive 'gearwherein said gear rotates said shaft and slides in frictional engagementacross the surface of the boom on which said gear is bearing.

9. The hoisting apparatus of claim 8 wherein said boom is disposedvertically and supported from an overhead, said means for supportingsaid object is disposed on the lowerend of said shaft, a sleeve disposedcoaxial on said boom, said shaft is disposed within said sleeve, andsaid gear bears against the end of said sleeve.

10. The hoisting apparatus of claim 8 wherein said boom comprises atleast two telescoping sections.

11. The hoisting apparatus of claim 10 wherein track and follower meansare provided on said sections for guiding one of said sections intonesting position into an adjacent section, and take-up means areprovided for securely clamping said sections together automatically whensaid sections are stationary.

12. A hoisting apparatus in combination with an X-ray unit comprising avertical boom supported from over head, a sleeve fixed vertically to thelower end of said boom,'a tubular shaft rotatably disposed in saidsleeve, frictional drive meansdisposed between said shaft andsaidsleeve, said X-ray unit fixed to the lower end of said shaft, saidshaft and said X-ray unit fixed thereto being adapted and arranged forrotation about said boom axis, and a flexible conduit means extendingthrough said tubular shaft.

13. A hoisting apparatus in combination with an X-ray unit comprising atelescoping boom having at least two sections with one of said sectionsnesting within an adjacent section, said unit supported on one end ofsaid boom, said X-ray unit adapted and arranged so as to be capable ofrotation about said boom axis track and follower means on said sectionsfor guiding one of said sections within an adjacent section, said trackand follower means comprising a track on said inner section andfollowers on said outer section, said followers being disposed adjacentthe end of said outer section closest to said inner section, and take-upmeans for securely clamping said sections together automatically whensaid sections are stationary said take up means comprising a lever meansincluding a lever on which at least two of the followers in the form ofrollers are mounted, said lever pivotly mounted on said outer section,one of said track means disposed between two of the roller followers 011said lever, and means for applying a moment on said lever whereby saidfollowers bear firmly against said track.

14. A hoisting apparatus in combination with an X-ray unit comprising atelescoping boom having at least two sections with one of said sectionsnesting within an adjacent section, said unit supported on one end ofsaid boom, track and follower means on said sections for guiding one ofsaid sections within an adjacent section, take-up means for securelyclamping said sections together automatically when said sections arestationary, means for rotating said object about the axis of said boom,said means for rotating said object comprising a shaft disposed torotate about said axis, said shaft bearing against a drive gear, saiddrive gear bearing against said boom, means for rotating said drive gearwherein said gear rotates said shaft and slides in frictional engagementacross the surface of the boom on which said gearis bearing;

15. The apparatus of claim 14 wherein a sleeve is disposed coaxiallywithin the bottom end of said boom, said shaft is disposed within saidsleeve, and said gear bearing against the end of said sleeve.

16. The apparatus of claim 14 wherein said boom is disposed verticallyand said unit is disposed on the lower end thereof.

17. The apparatus of claim 14 wherein said track and follower meanscomprises a track on said inner section disposed adjacent the lower endof said outer section.

18. The apparatus of claim 17 wherein said take-up means comprisespreloaded followers.

19. A hoisting apparatus in combination with an X-ray unit comprising atelescoping boom having at least two sections with one of said sectionsnesting within an adja cent section, said unit supported on one end ofsaid boom, track and follower means on said sections for guiding one ofsaid sections within an adjacent section, take-up means for securelyclamping said sections together automatically when said sections arestationary, means for rotating said object about the axis of said boom,said means for rotating said object comprising a shaft disposed torotate about said axis, said shaft bearing against a drive gear, saiddrive gear bearing against said boom, means for rotating said drive gearwherein said gear rotates said shaft and slides across the surface ofthe boom on which said gear is bearing, said track and follower meanscomprising a track on said inner section and followers on said outersection, said followers being disposed adjacent the lower end of saidouter section, said take-up means comprising a lever means including alever on which at least two followers in the form of rollers aremounted, said lever pivotally mounted on said outer section, one of saidtracks disposed between two of said roller followers on said lever, andmeans for applying a moment on said lever where by said roller followersbear firmly against said track.

20. The apparatus defined in claim 19 wherein said lever means furtherincludes a pair of said levers with said roller followers engaging eachone of said tracks, and a spring attached to said pair of leversdisposed on the same side of said track.

21. The apparatus defined in claim 20 wherein said spring is attached toone of said levers of said pair closer to its pivot mount than saidspring is attached to other of said levers whereby a greater moment isplaced on said other lever than on said one lever.

22. The apparatus defined in claim 21 wherein at least said lever meansfurther includes a pair of said levers with said followers engaging eachone of said tracks, and a spring attached to the ends of said pair oflevers and disposed on the same side of said track.

23. The apparatus defined in claim 22 wherein said boom comprises atleast three telescoping sections, and positive control means areprovided to move at least three adjacent sections in a controlled mannerwith re spect to each other.

24. The apparatus defined in claim 23 wherein said positive controlmeans comprises two spaced pulleys on a center section, and an endlessrope engaging said pulley with the outer and inner section from saidcenter section being attached to said rope.

25. A hoisting apparatus in combination with an X-ray unit comprising atelescoping boom having at least two sections, one of said sectionsnesting within an adjacent section, said unit supported on one end ofsaid boom, track and follower means on said sections for guiding one ofsaid sections within an adjacent section, take-up means for securelyclamping said sections together automatically when said sections arestationary, a sleeve fixed vertically to the lower end of said boom, ashaft rotatably disposed in said sleeve, a flange on said shaft bearingagainst said sleeve, said X-ray unit fixed to lower end of said shaft,said track and follower means comprising a track on said inner sectionand followers on said outer section, said followers being disposedadjacent the lower end of said outer section, said take-up meanscomprising a lever means including a lever on which at least twofollowers are mounted, said lever pivotally mounted on said outersection, one of said tracks disposed between two of said followers onsaid lever, and means for applying a moment on said lever whereby saidfollowers bear firmly against said track.

26. The apparatus defined in claim 25 wherein said followers are in theform of rollers.

27. A hoisting apparatus comprising a telescoping boom having at leastthree sections, said sections being coaxially disposed and including aninner section and an adjacent outer section, means for supporting anobject on one end of said boom, means for rotating said object about theaxis of said boom, track and follower means on said sections for guidingsaid inner section within said adjacent outer section; and take-up meansfor securely clamping said inner and outer sections togetherautomatically when said sections are stationary, and positive controlmeans being provided to move said three sections of said boom in apositive controlled manner with respect to each other.

28. The apparatus defined in claim 27 wherein said positive controlmeans comprises two spaced pulleys mounted on said inner section, anendless rope engaging said pulley, and said two other sections of saidthree sections being attached to said rope.

29. A hoisting apparatus comprising a telescoping boom having at leasttwo sections including an inner section nesting within an adjacent outersection, means for supporting an object on one end of said boom, meansfor rotating said object about the axis of said boom, track and followermeans on said sections for guiding said inner section within saidadjacent outer section, and take-up means for securely clamping saidinner and outer sections together automatically when said sections arestationary, said means for rotating the object about the axis of saidboom including a friction bearing portion.

30. The apparatus defined in claim 29 wherein said means for rotatingsaid object about the axis of said 10 boom including said frictionbearing portion comprises a shaft disposed to rotate about said axis,said shaft bearing against a drive gear, said drive gear bearing againstsaid boom and means for rotating said drive gear, said gear rotatingsaid shaft and said gear sliding on the surface of the boom on whichsaid gear is bearing.

31. A hoisting apparatus in combination with an X-ray unit comprising atelescoping boom having at least two coaxial sections with one of saidsections nesting within an adjacent section, said unit supported on oneend of said boom, track and follower means on said sections for guidingone of said sections Within an adjacent section, take-up means forsecurely clamping: said sections together automatically when saidsections are stationary, a sleeve fixed vertically to the lower end ofsaid boom,

a shaft rotatably disposed in said sleeve, a flange on said shaftbearing against said sleeve, said X-ray unit fixed to the lower end ofsaid shaft.

References Cited by the Examiner UNITED STATES PATENTS 2,265,086 12/41Spiro 308--6 X 2,659,827 11/53 Scag et a1 250-91 2,737,596 3/56 Haupt etal 250-91 2,835,520 5/58 Schiring et a1.

2,841,717 7/58 Kizaur 250-92 2,876,362 3/59 Foderaro 25091 3,061,11110/62 Riemenscherider 212-21 RALPH G. NILSON, Primary Examiner.

1. A HOISTING APPARATUS COMPRISING A TELESCOPING BOOM HAVING AT LEASTTWO COAXIAL SECTIONS INCLUDING AN INNER SECTION NESTING WITHIN AN OUTERADJACENT SECTION, MEANS FOR SUPPORTING AN OBJECT ON ONE END OF SAIDBOOM, MEANS FOR ROTATING SAID OBJECT ABOUT THE AXIS OF SAID BOOM TRACKAND FOLLOWER MEANS ON SAID SECTIONS FOR GUIDING SAID INNER SECTIONWITHIN SAID ADJACENT OUTER SECTION, AND TAKEUP MEANS FOR SECURELYCLAMPING SAID INNER AND OUTER SECTIONS TOGETHER AUTOMATICALLY WHEN SAIDSECTIONS ARE STATIONARY SAID TAKE-UP MEANS ALSO SUBSTANTIALLY RESTRICTTRANSVERSE RELATIVE MOTION, WITH RESPECT TO THE BOOM AXIS, BETWEEN SAIDSECTIONS BOTH WHEN SAID SECTIONS ARE MOVING RELATIVE TO ONE ANOTHER ANDWHEN SAID SECTIONS ARE STATIONARY.